1. Field of the Invention
This invention relates to shuttleless looms of the type in which a weft is inserted into a warp shed by the reciprocal movements of its carrying holder, and more particularly, to a flexible type rapier loom in which the reciprocal movements of the weft carrying holder are effected by a reciprocally rotatable wheel and a flexible tape having elasticity.
2. Description of the Prior Art
The general construction of the flexible type rapier loom will be described with reference to FIGS. 1 and 2. The aforementioned weft holder 7 is fixed to one end of an elastic flexible tape 1, which assumes a straight shape under its normal condition, so that it is moved back and forth within the shed while having the aforementioned tape 1 guided by a straight guide 11 which is fixed to a loom body 10. The other end of the tape 1 is fixed to the outer circumference of a wheel 2 which is rotatably mounted in a supporting bracket 12 of a wheel cover fixed to the loom body 10. Thus, the tape 1 is wound on the outer circumference of the wheel 2 by the rotation of the wheel 2 in one direction or unwound therefrom by the rotation of the wheel 2 in the other direction, while being guided by a tangential guide 9 fixed to the loom body 10, so that it is let off tangentially of the wheel 2 thereby to move the aforementioned weft holder back and forth within the shed.
In order that the elastic flexible tape may be wound in a curved shape on the outer circumference of the wheel and let off tangentially of the wheel, generally speaking, as shown in FIG. 2, guides 13, 14, 15, 16, 17, 18 and 19 having a slightly larger curvature than that of the outer circumference of the wheel are fixed outside of the wheel circumference to the supporting bracket 12 so that the tape 1 is guided by guides 13 to 17 as well as the aforementioned tangential and straight guides 9 and 11.
According to this construction, the tape 1 is slid, while partially abutting against the inner sides of the guides 13 to 17 and the tangential guide 9, without being moved back and forth in contact with the outer circumference of the wheel 2, in accordance with its reciprocal movements due to the reciprocal rotations of the wheel 2, mainly because of the centrifugal force during its movements, its reaction when it is curved into an arcuate shape along the wheel, as well as the components of forces at the fixed point of the tape 1 to the wheel 2 when it is to be let off and wound. Those abutting slides produce high frictional sliding so that the tape is heated, the tape and the guides are worn, and the power loss is very high. This influence becomes the more prominent as the machine is driven at the higher speed, thus inviting one of the major causes for preventing the speed of the rapier loom from being increased.
For purposes of knowing that influence, the Inventors have conducted the following experimental exemplifications. More specifically, the mechanism shown in FIG. 2 was attached to the rapier loom and was driven so that the forces for the stationary guides 13, 14, 15, 16 and 17 to be pressed at a right angle by the tape during the drive were measured. In these experiments, the loom was run without the use of the warp and weft. One example of the experiments is illustrated in FIG. 3. As is apparent from FIG. 3, the stationary guide located the closer to the fixed end of the tape 1 to the wheel 2, is subjected to the stronger pressing force.
On the other hand, the results in which the power A consumed by the rapier loom under its full load running condition and the power B consumed by the same under the condition having the tape removed were measured with the R.P.M. of the machine being varied are plotted in FIG. 4. As is apparent from the FIGURE, the power consumption A during the full load running operation is markedly higher than the power consumption B in case the machine is run with the tape being removed, and the difference A-B is the power consumption due to the movements of the tape and is mostly the power loss due to the sliding frictional resistance between the tape and the stationary guides 13 to 17, i.e., a kind of the braking action of the stationary guides upon the run of the tape.
Upon examination of FIG. 4, it is found that more than 50% of the power loss during the full load running operation comes from the movements of the tape. Since, moreover, most of the power loss due to the movements of the tape is the sliding frictional resistance, in order to improve the power consumption and the durabilities of the tape and the stationary guides, it can be said that reduction in the frictional resistance between the tape and the stationary guides is remarkably effective and leads to the speed-up of the rapier loom.
As a trial to reduce the aforementioned sliding frictional resistance, there is an invention which is disclosed in U.S. Pat. No. 2,810,403. According to the invention disclosed, a rim made of a non-magnetic thin plate is fixed to the outer circumference of the aforementioned wheel in a manner to overhang in an annular shape at one side thereof, and one end of the aforementioned tape is fixed to the rim so that it may be wound on the circumference of the rim. On the other hand, a number of magnets (e.g. permanent magnets or electromagnets) are attached in a circular shape to the supporting bracket which is fixed to the loom body while also acting as a fitting for a wheel cover, and are arranged on the diametrically inner side of the aforementioned rim such that both poles are made to face the inner side of the aforementioned rim at a slight spacing therefrom. According to the prior art thus constructed, the magnetic tape is attracted to and retained on the outer circumference of the rim, when it is curved along the curvature of the rim of the wheel, by the attracting forces of the magnets, which are fixed to the bracket at the diametrically inner side positions of the rim, so that the tape is kept away from contact with the stationary guide, when it is located on the curvature of the rim, thus intending to eliminate the sliding frictional resistance inbetween. A considerable spacing is, however, required between the tape and the magnets for eliminating the sliding frictional resistance between the reciprocating tape and the stationary magnets, in other words, the sliding frictional resistance between the wheel or the rim and the magnets.
Generally speaking, in case a magnetic member is attracted and held in position by making use of the attracting force of a magnet, this attracting force of the magnet is decreased in proportion to the square of the distance of the gap, if any, between the magnetic member and the magnetic poles of the magnet. Therefore, the decrease in the attracting force in this case is surprising as compared with the case in which the magnetic member is attracted in contact with the magnetic poles. In the invention disclosed in the aforementioned United States Patent, a considerable attracting force is required for holding the metal tape having a width of 25 mm and a thickness of 0.8 mm, which is being generally used at present, on the outer circumference of the rim along the curvature of the wheel. If, moreover, the wheel is swung back and forth in accordance with the drive of the loom, the tape is oscillated diametrically and circumferentially of the wheel so that the spacing from the poles of the magnets fixed to the supporting bracket is varied. As a result, the attracting forces of the magnets are so markedly varied as to make it difficult to hold the tape on the outer circumference of the rim of the wheel.